Abstract
Abstract: By analyzing the data of urban air pollutant measurements from 2013 to 2015 in Nanjing, East China, we found that the correlation coefficients between major atmospheric compound pollutants PM2.5 and O3 were respectively 0.40 in hot season (June, July and August) and −0.16 in cold season (December, January and February) with both passing the confidence level of 99%. This provides evidence for the inverse relations of ambient PM2.5 and O3 between cold and hot seasons in an urban area of East China. To understand the interaction of PM2.5 and O3 in air compound pollution, the underlying mechanisms on the inversion relations between cold and hot seasons were investigated from the seasonal variations in atmospheric oxidation and radiative forcing of PM2.5 based on three-year environmental and meteorological data. The analyses showed that the augmentation of atmospheric oxidation could strengthen the production of secondary particles with the contribution up to 26.76% to ambient PM2.5 levels. High O3 concentrations in a strong oxidative air condition during hot season promoted the formation of secondary particles, which could result in a positive correlation between PM2.5 and O3 in hot season. In cold season with weak atmospheric oxidation, the enhanced PM2.5 levels suppressed surface solar radiation, which could weaken O3 production for decreasing ambient O3 level with the low diurnal peaks. Under the high PM2.5 level exceeding 115 μg·m−3, the surface O3 concentration dropped to 12.7 μg·m−3 at noon with a significant inhibitory effect, leading to a negative correlation between PM2.5 and O3 in cold season. This observational study revealed the interaction of PM2.5 and O3 in air compound pollution for understanding the seasonal change of atmospheric environment.
Highlights
With the rapid economic development and accelerating urbanization process, a lot of energy is consumed, increasingly releasing pollutant emissions into ambient air in urban regions of Atmosphere 2017, 8, 59; doi:10.3390/atmos8030059 www.mdpi.com/journal/atmosphereChina, where air pollution has been changing from coal-smoke to compound-polluted type.Air compound pollution brings serious environment and health problems in urban areas of China [1,2].As representative pollutants of air compound pollution, ozone (O3 ) and fine particles (PM2.5 ) in ambient atmosphere, are becoming a pervasive air quality problem facing China
The proportions calculated with Equation (1) could reflect the seasonal variations in atmospheric environment connecting with PM2.5 and O3 pollution over the urban area in cold and hot seasons (Tables 1 and 2)
It should be pointed out that the contributions of secondary PM2.5 particles to air pollution were qualified by adopting the assessment approach of Chang et al [38] to understand the positive correlation between PM2.5 and O3 during hot season in this study, which could reflect the role of atmospheric oxidation in secondary particle formation with the discrepancies from previous studies on other urban regions [19,39]
Summary
With the rapid economic development and accelerating urbanization process, a lot of energy is consumed, increasingly releasing pollutant emissions into ambient air in urban regions of Atmosphere 2017, 8, 59; doi:10.3390/atmos8030059 www.mdpi.com/journal/atmosphere. With a high density of population, the prosperity of industrial activity and transportation, Nanjing, a major urban area in Yangtze River Delta region, has been experiencing air compound pollution in recent years [8,9,10]. Secondary organic and inorganic aerosols generated from oxidation reactions comprise a significant fraction of particulate matters with high implications for air pollution in China [19]. Based on three-year (2013–2015) environmental and meteorological monitoring data in Nanjing, a major urban area in East China, this study attempted to comprehensively explore the relation of PM2.5 and O3 and its seasonal change to deepen the understanding of air compound pollution in China with the implications on atmospheric environment changes
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